The water content of ethanol obtained in industrial production can be removed according to distillation, but the concentration value of ethanol is above 95.5%, and it can not be further separated. Why is that? The two produce an azeotrope (melting point 78.1 ° C), and in further distillation, the two are steamed at this proportion throughout. If you want to further increase the concentration value of ethanol, only want another way.

A method often mentioned in junior high school exam questions: mixing quicklime powder with ethanol, distilling (water bath), can prepare anhydrous ethanol. To put it bluntly, anhydrous ethanol, that is, the concentration value of ethanol is above 99.5%. The specific way of preparing anhydrous ethanol is not so funny. Here is a brief introduction to the common ways of preparing anhydrous ethanol.

Preparation methods: azeotropic distillation, extractive distillation, molecular sieve desiccation, membrane separation technology, the above four have already completed industrial production and manufacturing; Lime powder method, potassium acetate and sodium acetate solution desiccation method, vacuum pump distillation method, cassava starch adsorption method, ion exchange method epoxy resin desiccation method, sodium, magnesium drying method, etc.

I. Industrial production and preparation method

1, azeotropic distillation method

The way is: ethanol - water - benzene (or cyclohexane, pentane, etc., known as the inducer) is put into the azeotropic distillation device, in which the water - ethanol - benzene produces ternary azeotrope (constant melting point 64.9℃) is steamed, all the water is taken away, and the distilled ethanol is nearly pure.

2, membrane separation technology

The spread rate of the components is not the same according to the membrane, the spread of the fast first according to the membrane, the spread of the slow is very little or not through the membrane, and the purpose of separating the components can be achieved. There are two ways, one is to let the liquid become vapor according to the membrane, and the other is to vaporize the liquid and let the vapor separate out according to the membrane.

3, molecular sieve desiccation method

The molecular diameter of water is 2.6A (1A =10^ -10 meters), the molecular diameter of ethanol is 4.7A, and the molecular sieve with a diameter of 3A is used to heat the solution into vapor, so that the water will be obviously adsorbed according to the molecular sieve, and the high purity ethanol can be obtained when cold.

4. Extractive distillation

The ethanol-water is mixed with the glycol solution of salt (potassium acetate, calcium chloride, copper chloride, sodium oxide, etc.) or alkali (sodium hydroxide solution, ferric chloride solution, etc.) added to the management system, together with the rectification tower, the concentration value of ethanol is more than 99.5%.

2. Laboratory preparation of anhydrous ethanol (99.5%) or positive ethanol (99.95%)

1. CaO Method

Anhydrous ethanol can be obtained by placing the newly forged CaO in 95% ethanol, cooling it back for a period of time, and then distilling it.

2, magnesium dry mania method to prepare positive ethanol

The magnesium strip (magnesium powder) and iodine are added to anhydrous ethanol, and the temperature is first heated and the flow is returned to the reaction thoroughly, and then the ethanol is distilled.

3, sodium dry mania method to prepare positive ethanol

Sodium is reflected with anhydrous ethanol, and then diethyl phthalate (or diethyl succinate) is added, first flowed back, and then distilled to confirm ethanol.